Move log.setup to Bootstrap and use cfg.CONF opts

This patch uses cfg.CONF as ConfigOpts in common/config instead of
creating a new instance of it. This is needed since most of Oslo's
modules use the global CONF object to register their config parameters.

The patch also moves log.setup call into Bootstrap and calls it after
configs are loaded.

Fixes bug: #1190524

Change-Id: Ib601418a7dbcad84c79b640b93bc5798ec4a62c4